The present invention relates to printing technology. More specifically, it relates to an improved ink composition for use in inkjet printers. Even more specifically, it relates to the use of an improved ink composition, equipment, and methods to produce permanent printed images on a variety of substrates by an inkjet printer.
Along with the computerization of offices in the 1980""s came electronically controlled non-impact printers such as the ink jet and laser printers. Drop-on-demand inkjet printers can be piezo or thermal (bubble jet). In piezo ink jet systems, ink droplets are ejected by an oscillating piezo crystal. However, the thermal ink jet dominates the drop-on-demand office ink jet market. In this system, rapid heating behind the ink nozzles causes a bubble of vapor to form in the ink. The resulting bubble expansion and ink ejection from the inkjet printer cartridge causes printing to appear on the substrate.
Full-color inkjet printers are more common than color lasers and are much more economical. The main advantage of inkjet printers over lasers and other non-impact printing techniques include their low cost and simplicity. Thermal inkjet systems are capable of dispensing ink rapidly and accurately. The technology of this and other inkjet systems are discussed in the Chemistry and Technology of Printing and Imaging Systems, edited by P. Gregory, published by Chapman and Hall, 1996. Representative thermal inkjet systems and cartridges are discussed in U.S. Pat. No. 4,500,895 to Buck et al., U.S. Pat. No. 4,513,298 to Scheu, and U.S. Pat. No. 4,794,409 to Cowger et al., which are all hereby incorporated by reference.
The technology of inkjet printers has undergone many changes and improvements since they first appeared. Research has been conducted to ensure that the images produced are of consistent high quality. Thus, it is important that the images be waterfast and do not smear, smudge, run, or the like when exposed to chemical or mechanical abrasion. Non-smearing of the image when portions of the printed page are highlighted with colored markers is of particular interest. Oftentimes, the image produced by the inkjet printer on paper is not satisfactorily fixed and smears, blurring the printed image when subjected to highlighting. This type of image is not regarded as permanent.
Image permanence is defined as transference of color from the substrate when the image printed thereon is subjected to chemical and mechanical abrasion. Highlighting is oftentimes the form of chemical and mechanical abrasion experienced. This transference of color is measured by optical density (mOD). More permanent images have lower milli-Optical Density (mOD) values.
Another desired feature of printed images is light fastness. As used herein, light fastness will mean that the images do not fade when exposed to light. Light fastness is another measure of permanence as used herein. Light fastness is measured by exposing printed images to intense light in light chambers (fadomers) and comparing print density before and after the exposure.
There have been many past attempts at improving the permanence of water-based inkjet printing systems. Included among these attempts are U.S. Pat. No. 5,549,740 to Takahashi et al., U.S. Pat. No. 5,640,187 to Kashiwakazi et al., and U.S. Pat. No. 5,792,249 to Shirota et al. which utilizes an additional or xe2x80x9cfifthxe2x80x9d pen to apply a colorless fluid on to the substrate. As will be seen in the comparative testing, the mOD values for the images printed thereon are quite high.
In U.S. Pat. No. 5,831,655 Asawa discloses an ink jet recording apparatus that is concerned with forcibly drying the ink deposited on a recording medium so that the image is not scratched when contacted with other objects or blurred because of the quality of paper used.
In the ""655 patent, the ink droplet is comprised of a saccharide, plus other ingredients commonly used in inks such as colorant, resin, surfactant and water. There is no mention or values measured for image permanence on various types of paper substrates. Nor is there any mention of measurement of permanence of the images after subjection to chemical and mechanical abrasion using optical density measurements.
Another highly efficient printing system in common use currently is laser printers. In a laser printer or copier, light from a laser beam is used to discharge areas of a photoreceptor to create an electrostatic image of the page to be printed. The image is created by the printer controller, a dedicated computer in the printer, and is passed to the print engine. The print engine transcribes an array of dots created by the printer controller into a printed image. The print engine includes a laser scanning assembly, photoreceptor, toner hopper, developer unit, Corotrons, discharge lamp, fuser, paper transport, paper input feeders, and paper output trays.
The final stage of laser printing or copying is to fix toner onto the paper. Toner is very fine plastic powder, which is transferred from the photoreceptor. Once transferred from the photoreceptor, it lies on the paper in a very thin coating with nothing to hold it in place. In order to fix the toner to the paper, it is heated by passing between a pair of very hot rollers, so that the plastic melts around the fibers of the paper and is xe2x80x9cfusedxe2x80x9d into place. The image is now fixed permanently onto the paper.
The fuser of a typical laser printer is of particular interest to the printing system of this invention. In these systems, fusing or melting the polymeric resin in which the colorant is embedded converts the discrete toner particles into an amorphous film. This film becomes the permanent image that results in electrophotographic copy or laser printed copy. However, the laser printer toners are incompatible with water. Since most inkjet materials are water-based, it is not possible to use laser toners in inkjet printers, and, therefore, Inkjet technology has not yet found a way to make the printed image permanent.
Another printing technology that is inherently more permanent than water-based inkjet are hot-melt inks. These materials are solid at room temperature and are similar to wax crayons. The colorants used in these materials are solvent dyes that are soluble in the ink vehicle or pigment dispersions. Like laser toners, these materials are incompatible with the inks used in inkjet printing.
In U.S. Pat. No. 5,817,169 Sacripante discloses a hot melt ink composition which uses oxazoline as a vehicle used for the colorant in inkjet printing processes. One of the advantages of this technology is the waxy nature of the hot melt ink creates images that are more waterfast and may be successfully utilized on plain papers. This technology is in contrast with the instant invention, which utilizes an ordinary waterborne, liquid four-color ink pen set.
Accordingly, a need remains for a printing system using water-based inkjet technology which produces permanent images. These permanent images will be consistent and stable with respect to a variety of printed substrates. An ideal situation would be combining the convenience and safety of aqueous inkjet inks with the permanence of electrophotographic copies. The present invention satisfies this in a unique manner which is described herein.
The invention relates to a fusible material that is added to aqueous ink formulations and provides an improved printed image that is especially suitable for use with inkjet technology.
Further this invention encompasses methods for printing permanent images using inkjet technology which comprises a fusible material formulated with the four-pen ink-set commonly found in water-based color inks used in inkjet printing. The fusible material of the present invention can be formulated as a colorless fluid applied either before or after the color inks are applied to the substrate. The images and print quality achieved by the use of such a fusible material in waterborne ink formulations are comparable in permanence and print quality to those of laser printers and copiers. These images, in black or color, are permanent and will not smear, smudge, run, or the like when exposed to mechanical or chemical abrasion.
Also presented herein are printing devices incorporating the ejection of droplets of fluid on to a substrate and producing a printed page with a permanent image. In this embodiment, the inkjet printer is equipped with a fuser. The fuser of a typical laser printer is commercially available and has been modified for use in an inkjet printer to provide superior image quality and permanence to the printed substrate. In a similar fashion, incandescent lamps or other suitable heating means may be employed.
Moreover this invention provides an improved printing system which produces consistent high quality printed images regardless of the type or quality of printing substrate, such as different types or qualities of paper or transparent sheets used to make overhead projections (transparencies), being used.
In accordance with the foregoing, the present invention relates to an improved printing system for producing stable, water-fast, permanent printed images. The system combines the ease and versatility of traditional water-based inkjet technology with the permanence of laser printing or copying technology (electrophotography).
These and other features and advantages of the current invention will be described below in the Detailed Description of the Invention and succinctly outlined in the claims that follow.
The present invention relates to an improved printing system that is capable of producing permanent images on a variety of substrates using waterborne inkjet printing. The invention allows for the inclusion of fusible materials into water-based inks and demonstrates the increased permanence of the images produced.
The standard ink set components known and used in inkjet printers comprise four colors of ink, namely yellow, magenta, cyan, and black. This set is often referred to as a xe2x80x9cfour penxe2x80x9d system. These four pens are made of various materials and are formulated into aqueous inks.
Each of the standard four pens contains a water-soluble or insoluble dye having an anionic group, or when a pigment is used as a colorant, the pigment is either self-dispersing or is aided in solubility by a dispersant. In many applications, both pigments and dyes are used for coloring the ink. The ink formulation also typically contains water, a water-miscible solvent, and other components such as a biocide, viscosity modifiers, a pH adjuster, preservatives, surfactants, and the like.
Pigmentsxe2x80x94When a pigment is used as a coloring material in the ink composition of the present invention, the amount of pigment used is within the range from about 0.5 to about 20 weight percent. A more preferable range of pigment ranges from about 1 to about 15% by weight, still more preferably is a range of from about 2% to about 12% by wt.
An example of a pigment used for a black ink is carbon black. The carbon black may be produced by either a furnace or channel method. The primary particle size of this material ranges from 15 to 40 xcexcm, specific surface area is 50 to 300 m2/g, and has oil absorption from 40 to 150 ml/100 g, the volatile component is 0.5 to 10%, and the pH value may range from 2 to 9. Examples of suitable commercially available carbon blacks include No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MAand, MA8, No. 2200B, Raven 1255, Regal 400R, Regal 330R, Regal 660 R, Mogul L, Color Black FW1, Color Black FW18, Color Black S170, Color Black S150, Printex 35, and Printex U.
In this invention, the black colorants that were employed include Novofil Black BB-03, and Hostafine Black TS. The Novafil material is a pigment that is approximately 27% pigment dispersion based on anionic dispersing agents. It contains C.I. Pigment Black 7, carbon black and is an ultrafine pigment dispersion suitable for all water based inkjet application. These pigments are available from Clairiant Corp., Coventry, R.I.
Hostafine Black TS contains hydrophilic ultrafine pigment dispersions based on non-ionic dispersing and wetting agents. It contains carbon black and has a pigment concentration of 33%.
Other black colorants which may be used include those listed in the Color Index and in Textile Chemist and Colorist reference publications. Water-soluble black colorants are commercially available from colorant vendors such as Cabot Corporation, Orient Chemical, and other manufacturers. Surface modified colorants from these manufacturers are initially water insoluble colorants which, by certain modifications, are solubilized or stabilized as fine dispersions in water to prevent agglomeration. See U.S. Pat. Nos. 5,707,432; 5,630,868; 5,571,311; and 5,554,739 for a discussion of modified carbon black pigments and methods of attaching functionalized groups to aid in their solubility.
Examples of pigments used for a yellow ink include C.I. Pigment Yellow 1, C.I. Pigment Yellow 2, C.I. Pigment Yellow 3, C.I. Pigment Yellow 13, C.I. Pigment Yellow 16, C.I. Pigment Yellow 83, and the like. Examples of pigments used for magenta ink include C.I. Pigment Red 5, C.I. Pigment Red 7, C.I. Pigment Red 12, C.I. Pigment Red 48 (ca), C.I. Pigment Red 48 (mn), C.I. Pigment Red 57 (Ca), C.I. Pigment Red 112, C.I. Pigment Red 122, and the like. Examples of pigments used for a cyan include C.I. Pigment Blue 1, C.I. Pigment Blue 2, C.I. Pigment Blue 3, C.I. Pigment Blue 5:3, C.I. Pigment Blue 16, C.I. Pigment Blue 22, C.I. Vat Blue 4, C.I. Vat Blue 6, and the like. Pigments whose performance properties are satisfactory when formulated for the present invention are considered to be within its scope.
In the instant invention, colorants used include Hostafine Rubine F6B and Hostafine Blue B2G available from Clariant, Coventry, R.I. Hostafines are hydrophilic ultrafine pigment dispersions based on nonionic dispersing and wetting agents, available in all colors. In this disclosure, Hostafine Rubine F6B is magenta with a 40% pigment content. Hostafine Blue B2G is blue with 40% pigment as well. These colorants are manufactured for suitability with water-based inkjet inks.
Any pigment, dye, or pigment-resin system available and compatible with the other formulated ingredients of the fusible material of this invention may be used as colorants. An important factor that the formulator must keep in mind is thermal instability exhibited by certain tri- and tetrakis-azo dyes. Such thermal instability may lead to charring of insoluble deposits (kogation), which is to be avoided.
Dyesxe2x80x94Dyes, whether water-soluble or water-insoluble, may be employed in the practice of the present invention. Examples of water-soluble dyes include the sulfonate and carboxylate dyes, specifically, those that are commonly employed in ink-jet printing. Specific examples include: Sulforhodamine B (sulfonate), Acid Blue 113 (sulfonate), Acid Blue 29 (sulfonate), Acid Red 4 (sulfonate), Rose Bengal (carboxylate), Acid Yellow 17 (sulfonate), Acid Yellow 29 (sulfonate), Acid Yellow 42 (sulfonate), Acridine Yellow G (sulfonate), Nitro Blue Tetrazolium Chloride Monohydrate or Nitro BT, Rhodamine 6G, Rhodamine 123, Rhodamine B, Rhodamine B Isocyanate, Safranine O, Azure B, Azure B Eosinate, Basic Blue 47, Basic Blue 66, Thioflacin T (Basic Yellow 1), and Auramine O (Basic Yellow 2), all available from Aldrich Chemical Company. Examples of water-insoluble dyes include azo, xanthene, methine, polymethine, and anthroquinone dyes. Specific examples of water-insoluble dyes include Ciba-Geigy Orasol Blue GN, Ciba-Geigy Orasol Pink, and Ciba-Geigy Orasol Yellow.
The ink formulation comprises a colorant plus a vehicle. A typical formulation for an ink useful in the practice of this invention includes the colorant, present in about 0.5 to about 20 weight percent, one or more co-solvents, present from 0 to 50 weight percent, one or more water-soluble surfactants, present in about 0.1 to 40 weight percent, one or more high molecular weight colloids present in from 0 to about 3 weight percent. The balance of the formulation is purified water. The colorless fluid is similar except for the absence of a colorant.
One or more co-solvents may be added to the formulation of the ink of this invention. Classes of co-solvents include, but are not limited to, aliphatic alcohols, aromatic alcohols, diols, glycol ethers, polyglycol ethers, caprolactams, formamides, acetamides, and long chain alcohols. Examples of such compounds include primary aliphatic alcohols, secondary aliphatic alcohols, 1,2-alcohols, 1,3-alcohols, 1,5-alcohols, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higher homologs of polyethylene glycol alkyl ethers, N-alkyl caprolactams, unsubstituted caprolactams, both substituted and unsubstituted formamides, both substituted and unsubstituted acetamides, and the like.
One class of preferred co-solvents that provides water miscibility to polymers is glycols. A particularly preferred glycol is polyethylene glycol, commonly abbreviated as PEG. Polyethylene glycol is hydrophilic.
A preferred surfactant employed in the present invention includes Noigen10(trademark). Noigen10(trademark) is a commercially available polymerizable surfactant available from the Montello Company of Tulsa, Okla. Noigen10(trademark) contains polyethylene glycol as a hydrophilic group and an octyl or nonyl phenol as a hydrophobic group. This type of surfactant, which can accommodate both hydrophobic and hydrophilic moieties, is a preferred ingredient in the formation of the fusible material of this invention.
However, other water-soluble surfactants may be employed in the formulation of the vehicle of the ink of this invention. The purpose of surfactants as described herein is to facilitate the miscibility of the ingredients of the ink composition. This is especially important if the fusible material of the ink composition contains both hydrophilic and hydrophobic groups. The surfactant(s) used are known by those skilled in the art of ink formulation and may be alkyl polyethylene oxides, alkyl phenyl polyethylene oxides, polyethylene oxide block copolymers, acetylenic polyethylene oxides, polyethylene oxide (di)esters, polyethylene oxide amines, protonated polyethylene oxide amines, protonated polyethylene oxide amides, dimethicone copolyols, substitued amine oxides, and the like. The amount of surfactant added to the formulation of this invention may range from less than one to about 10 weight percent. A more preferred amount is from 1 to about 3 weight percent.
Consistent with the formulation of this invention, various other additives may be employed to optimize the properties of the ink composition for specific applications. Examples of these additives are those added to inhibit the growth of harmful microorganisms. These additives may be biocides, fungicides, and other microbial agents which are routinely used in ink formulations. Examples of suitable microbial agents include, but are not limited to, Nuosept (Nudex, Inc.), Ucarcide (Union carbide Corp.), Vancide (R.T. Vanderbilt Co.), and Proxel (ICI America).
Sequestering agents such as EDTA (ethylene diamine tetra acetic acid) may be included to eliminate the deleterious effects of heavy metal impurities, and buffer solutions may be used to control the pH of the ink. Viscosity modifiers may also be present, as well as other additives known to those skilled in the art to modify properties of the ink as desired.
Each of the ingredients in the fusible material are present for a specific reason. For example, particle size and distribution, stability, surface tension, and various rheological properties are primarily controlled by the type and amount of surfactant employed.
Kogation refers to the charring of insoluble deposits on the printer""s heating elements. This clogs the inkjet print heads and is a problem common to thermal inkjet printers. For the fusible materials to be resistant to kogation, they must be soluble or miscible in the ink solvents at higher temperatures or in super heated solvent/water vapor. The invention allows inclusion of fusible materials in water based inks used in inkjet printing. These materials are soluble in the ink composition at higher temperatures or in super-heated solvent/water vapor. As used herein, superheating means the heating of a substance above the temperature at which a change of state would ordinarily happen without the change of state occurring.
The laser or copier toners generally contain polymers made from a variety of materials such as polyoxazolins, urethan/acrylic block or blended polymers, and polymers made from acrylate monomers, such as silicone acrylate (commercially available from the Sartomer Company, (Exton Pa.)), polycarbonates, polyvinylpyrrolidine, styrene-butadiene latexes, PEG-amine modified and/or diamine cross linked polyene-maleic anhydride such as ethylene maleic anhydride or octadecene-maleic anhydride, or rosin-maleic anhydride polymers.
Most of the toners materials listed supra are hydrophobic polymers. They are present in electrophotography as small, discrete grains that outline the image on a substrate prior to fusion. As such, these materials have been incompatible with and not viable for use in water-based inkjet inks. This invention utilizes this type of hydrophobic material, heretofore incompatible with water, a co-solvent such as PEG, and a variety of other ingredients, in a waterborne ink formulation that creates permanent images or in a colorless fluid which may be applied either before or after the ink.
Among the properties of interest for applications of some of these toners include glass transition temperature (Tg) and melt index. As used herein, glass transition temperature (Tg) will mean the transition that occurs when a liquid is cooled to an amorphous or glassy solid. It also may be the change in an amorphous region of a partially crystalline polymer from a viscous, rubbery state to a hard or brittle one brought about by change in temperature.
The glass transition temperature, Tg, reflects the mechanical properties of polymers over a specified temperature range. Below Tg polymers are stiff, hard, brittle, and glasslike; above Tg they are relatively soft, limp, stretchable, and somewhat elastic. The Tg determines the performance of the polymer; below Tg the majority of the polymer chains have a relatively fixed configuration and little motion takes place in the polymer. Above Tg the polymer chain has sufficient thermal energy for rotation or oscillation. Thus the Tg temperature marks the onset of polymer mobility.
Chemical reactivity, mechanical and dielectric relaxation, flow, load-bearing capacity, hardness, tack, heat capacity, refractive index, thermal expansivity, creep, crystallization, and diffusion differ markedly below and above Tg. In this invention, Tg and melting temperature Tm may be used interchangeably.
The melt index (M.I.) refers to the number of grams of a thermoplastic resin at 190 degrees C. that can be forced through a 0.0825 inch (2.0955 millimeter) orifice in 10 minutes by a 2160 gram force. These definitions and those of related terms may be found in the McGraw-Hill Dictionary of Scientific and Technical Terms, 5th Edition, Edited by S. Parker, 1994.
Both the Tg and the M.I. reflect certain properties of polymeric materials over a specified temperature range. The properties of importance to the materials that impart permanence to inkjet images include such hardness, elasticity, and viscosity. In this invention, the materials which are used to improve permanence of the images produced by inkjet printing fluid have a Tg that may range from about 40 to about 140 degrees C. A more preferred range of glass transition temperatures will range from about 50 to about 90 degrees C. Melt index (M.I.) values for the instant materials may range from about 400 to about 3000 grams/10 minutes. A more preferred range may be from about 1800 to about 2500 grams/10 minutes. A still more preferred range is from about 2000 and 2250 g/10 min.
The fusible materials used in the instant ink formulations for permanence must be made soluble or mixable with the other waterborne ingredients in the ink. It has been found that hydrophobic materials which may be present in hydrophobic toners, can be combined in an aqueous system is to form emulsions or latexes. The fusible materials have successfully been synthesized and shown to perform in aqueous ink systems to produced images with the quality and permanence heretofore only achieved in electrophotography.
Presented herein are representative examples of syntheses of fusible materials that provide permanence to the images formed by the materials and processes of the instant invention. Acrylate esters such as methyl acrylate or methacrylate and methyl butylacrylate, along with vinyl aromatic monomers, such as styrene, were used to prepare polymers that are printed using inkjet technology and then fused after the image has been transferred to a substrate.
The monomers used to form such an emulsion polymer (or latex) may be an alkyl acrylate or methacrylate. These alkyl acrylates or methacrylates comprise alkyl groups with from one to about twelve carbon alkyl groups. Among these are included methyl methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate and the like. These monomers may be combined with a polymerizable surfactant with both hydrophobic and hydrophilic moieties, such as Noigen, noted above and a vinyl aromatic monomer to prepare polymers that are fusible after the image has been transferred to a substrate.
Among the vinyl aromatic monomers that are contemplated for inclusion in this invention are styrene, substituted styrene, divinyl benzene, vinyltoluene, vinyl naphthalene, polyvinylbenzenes, and isomers thereof. A preferred vinyl aromatic monomer is styrene.
The fusible material that imparts permanence to the printed substrate that is a product of this invention is not limited to emulsion polymers. In fact, the fusible material does not have to be polymeric. The fusible material may be launched as solutions, dispersions, emulsions, liposomes, vesicles, latexes or by any other means that can provide stable distribution of the materials in water.
As will be seen in the Examples, the images made permanent by the ink formulation of this invention are very resistant to smear. This allows enhanced image quality, demonstrated by the transfer of less than 100 mOD In this invention, mOD is measured by running a water-based yellow highlighter (Sanford xe2x80x9cMajor Accentxe2x80x9d Highlighting Marker high pH labeled xe2x80x9cFluorescentxe2x80x9d) across black lines printed on white bond paper. The amount of ink that smears from the lines relates directly to the permanence of the inkjet ink.
One of the ways to include the fusible material of this invention is to include it in a clear fluid that is not part of the four-color ink set. This technology is sometimes called a xe2x80x9cfifthxe2x80x9d pen. Fifth pen technology has been used to optimize image quality and water-fastness, but has not been successfully used to improve permanence. However, when using the 5th pen to eject the fusible material composition of this invention, the colorless, waterborne liquid coats the substrate and imparts permanence to the printed image.
When the fusible material of this invention is used in a colorless fluid 5th pen device, the amount of fluid used to impart permanence to the image may range from about 0.1 to about 4 times the amount of color ink(s) used in forming the image. In other words, there would be a minimum of one drop of colorless fluid applied to the substrate for every ten drops of ink applied. The colorless layer may be applied either over or under the color ink layer.
These clear fluids increase permanence of the color ink images by forming a pigment/polymer dispersant on the surface of the substrate. This reduces penetration of colorant in the media and helps improve the image color, optical density, and brightness of the printed image. The fusible material may also be added to any or all of the colored inks of the standard four-color pen set.
Fuser Devicexe2x80x94The printing system of this invention includes a printing apparatus that is equipped with suitable heating means. Heat fusion is most often the way that the image formed by toner particles used in electrophotography are fixed to the printed substrate. Most systems employ a heated roller to fix the image although any other means of supplying heat is included within the scope of this invention.
The heated roller is often a rubber roller impregnated with silicone oil which is preheated to about 90 degrees C. It may also be a metal roller heated with incandescent light or a lamp equipped with a reflector. Certain laser printers employ a ceramic heating element in the fusion stage. When the copier or printer is switched on, waiting time until the machine is ready to use is associated with heating the roller.
The heating means is designed to melt (or fuse) the toner on to the substrate. In high speed systems, flash fusion may be used. Flash fusion involves the use of heated lamps with a specific heat output are used to rapidly heat the toner which then adheres to the substrate. Fusers are commercially available from such companies that manufacture laser printers such as Hewlett-Packard, Canon, Ricoh, and Panasonic. In all cases, the toner particles used in electrophotography are hydrophobic.
A typical laser printer commonly available is the Hewlett-Packard Laser Jet 4L Printer. In the fusing stage, toner is fused into the substrate by heat and pressure to produce a permanent image. The substrate (usually paper) passes between a ceramic heating element protected by a thin Teflon sleeve and a soft pressure roller. This melts the toner and presses it into the substrate. Other laser printers use a halogen heating lamp and require frequent warm-up periods to maintain a minimum standby temperature.
Polymer Synthesisxe2x80x94Polymer syntheses were performed to control parameters such as rate of addition, extent of emulsification, and optimization of the reaction conditions to form a stable, reproducible emulsion polymer with satisfactory performance in the inkjet system of the present invention. The choice of catalyst was of importance as well.
Preliminary studies determined that the general reaction conditions to be used for the fusible material used in the inkjet formulation include use of azo catalyst, heating the reaction using a liquid heating jacket, stepwise addition of reactants in two separate phases, reaction time ranging between 5 and 10 hours, and others. A typical synthesis is described below:
The following examples and comparative examples are intended to illustrate the invention in further detail and not to limit the invention in any way whatsoever.